1. Field of the Invention
The present invention relates to a disk cartridge and a method of producing the same.
2. Description of the Related Art
A disk cartridge serves to store and protect a rotating disclike recording medium such as a magnetic disk, an optical disk, an opto-magnetic disk, or the like. The disk cartridge is constituted by upper and lower quadrangular shells in which a recording medium is rotatably disposed. A write/read window is formed in the upper and lower shells, and a head for writing or reading a recording medium signal (or write/read light) may be inserted through the window. This window is opened/closed by a slidable shutter made of a metal or resin. Sunken portions are formed in the respective upper and lower shells in an area over which this shutter slides. However, the thickness of the shells is not symmetric with respect to a center line passing through the write/read window and the rotation center of the rotary recording medium because the range of sliding of the shutter is located so as to be one-sided with respect to this center line.
FIG. 14 is an exploded perspective view of a flexible disk cartridge (hereinafter abbreviated to "FDC") of a 3.5-inch size.
FIG. 15A is a plan view of the upper shell of the FDC depicted in FIG. 14 when viewed from the inside thereof, and FIG. 15B is a sectional end view taken along the line 15B--15B. FIG. 16A is a plan view of the lower shell of the FDC depicted in FIG. 14 when viewed from the inside thereof, and FIG. 16B is a sectional end view taken along the line 16B--16B.
In these drawings, the thickness is exaggerated for convenience of construction of the drawings and for simplification thereof. This rule is also applied to the drawings showing embodiments of the present invention which will be described later.
The FDC comprises upper and lower quadrangular shells 1a and 1b made of a synthetic resin, and a shutter 3 made of a metal or resin. The upper and lower shells 1a and 1b have low walls at their peripheries. The upper shell 1a and the lower shell 1b are fixed to each other at four corners by ultrasonic welding or any other means. A magnetic disk 2 as a recording medium is rotatably disposed inside of these shells 1a and 1b.
The magnetic disk 2 is constituted by a rotation support 11 made of metal, and a doughnut-shaped sheet 13 attached to the support 11 and coated with a magnetic substance. A circular holding wall 10 and a circular hole 12 are formed in the center portion of the inner surface of the upper shell 1a and in the center portion of the lower shell 1b, respectively. The support 11 is loosely and rotatably fitted to the holding wall 10 and circular hole 12 so that the support 11 is positioned in the FDC. A hole 14 for chucking the magnetic disk 2 to a spindle of a flexible disk drive device (FDD) is formed in the support 11. Bulkheads 18a and 18b for guiding the peripheral edge of the magnetic disk 2 are formed in the inner surfaces of the upper and lower shells 1a and 1b, respectively.
Liners (not shown) made of nonwoven fabric or the like are stuck to the respective inner surfaces of the upper and lower shells 1a and 1b in order to prevent dust or the like from being deposited on the rotating magnetic disk 2 and to prevent the magnetic disk 2 from being damaged because of direct contact with the inner surfaces of the shells. Ribs 8a and 8b for supporting a cleaner (not shown) are formed on the insides of the upper and lower shells 1a and 1b, respectively.
A hole 9 for slidably attaching a write-protect tab (not shown) is formed at one corner of the lower shell 1b. A hole 16 for indicating the kind of the FDC is formed at another corner of the lower shell 1b. The holes 9 and 16 are surrounded by partition walls 17, respectively, in order to prevent dust or the like from entering into the FDC through these holes.
Write/read windows 4a and 4b through which a magnetic head (not shown) comes to write data into the magnetic disk 2 or to read data from the magnetic disk 2 are formed in one-side portion of each of the upper and lower shells 1a and 1b, respectively. A shutter 3 is provided to open/close the windows 4a and 4b. Sunken portions or recesses 5a and 5b are formed in the respective outer surfaces of the upper and lower shells 1a and 1b in a range in which the shutter 3 slides. The depth of each of the recesses 5a and 5b is substantially equal to the thickness of a constituent member of the shutter 3. In addition, recesses 7a and 7b for sticking a label or the like, arrows 18 for indicating the direction of insertion of the FDC, and so on, are formed in the outer surfaces of the upper and lower shells 1a and 1b.
The shutter 3 is composed of two shielding portions along the recesses of the upper and lower shells 1a and 1b, and a portion for connecting the shielding portions to each other. The shutter 3 is slidably attached onto the recesses 5a and 5b so that the upper and lower shells 1a and 1b are sandwiched by the shutter 3. Oblong windows 15a and 15b slightly larger than the write/read windows 4a and 4b are formed in the shielding portions of the shutter 3. The shutter 3 is normally urged toward one end of the recesses 5a and 5b by a spring (not shown) so that the windows 4a and 4b are closed by the shielding portions. When the FDC is inserted into the FDD, the shutter 3 is moved toward the other end of the recesses 5a and 5b by a shutter releasing mechanism in the FDD so that the windows 15a and 15b are made coincident with the windows 4a and 4b to thereby open the windows 4a and 4b.
Generally, the upper and lower shells 1a and 1b are formed by an injection molding method. Traces 6 of gates marked at the time of injection molding remain in the recesses 5a and 5b. Generally, gates for injecting molten resin are provided in unobstructive places, for example, at two points in the recesses 5a and 5b or at two points in the recesses 7a and 7b which are provided for sticking a label. Alternatively, gates may be provided at four points both in the recesses 5a and 5b and in the recesses 7a and 7b.
The windows 4a and 4b are formed in the upper and lower shells 1a and 1b in the lateral center positions, respectively. Assume now a center line C of the upper and lower shells 1a and 1b which passes through the center of the holding wall 10 or circular hole 12 and the center of the windows 4a and 4b. In the upper shell 1a depicted in FIGS. 15A and 15B, the recess 5a is located more in the left-sided position with respect to the center line C so that the thicker portion in the right side is wider than the thicker portion in the left side. In the lower shell 1b depicted in FIGS. 16A and 16B, the recess 5b is located more in the right-sided position so as to be eccentric with respect to the center line C, so that the thick portion in the left side is wider than the thick portion in the right side. Thus, the upper and lower shells 1a and 1b are not symmetric laterally with respect to the center line C because of the presence of the recesses 5a and 5b limiting the range of sliding of the shutter 3.
In molds for injection-molding these shells, there is a problem that a flow of resin coming into a cavity at the time of injection molding becomes unbalanced because of the lateral asymmetry in thickness of the shells. The imbalance of the flow of resin results in a weld line, formed when molten resins are merged and fused into one at the time of molding, not being located in the vicinity of the center line of the shells but located greatly eccentrically to the left or right.
FIGS. 17 and 18 show results of simulation of the flow of resin in a cavity in the case where molten resin is injected into the cavity through two gates 6, with respect to the conventional upper and lower shells, respectively. A larger amount of resin comes into the cavity from the thicker side where the flow resistance is small. It is apparent that the weld line WL is located greatly one-sided to the left in the case of the upper shell 1a and to the right in the case of the lower shell 1b.
Thus, there arises a phenomenon that the flow length of resin coming in through one gate is larger than the flow length of resin coming in through the other gate. As a result, the risk of a failure of complete filling with resin is heightened. Furthermore, there is a possibility that the molded shells may warp because of differences in packing density between the left and right resins.
The aforementioned problem can be solved if the thickness of the shells is made laterally symmetrical. It is however impossible to change the size of the slide portion of the shutter because the size is prescribed by JIS X6221 (equivalent to ISO 8860-1) or JIS X6223 (equivalent to ISO 9529-1).
There has been a proposal in which each shell is differentiated in thickness to provide a portion of resistance against the flow of resin to thereby control the flow of resin (Japanese Patent Unexamined Publication No. Hei-1-217780). This proposal is such that a portion of resistance against the flow of resin is provided in the vicinity of a resin filling end portion in order to solve the failure in which the flow of resin in the vicinity of a filling end portion goes round from the vicinity of the outer wall portion of a product to cause instability in thickness of this surrounded portion or formation of a hole. However, this proposal is not intended to control the overall filling of the shells with resin and not intended to solve the lateral imbalance of the filling with resin due to the presence of the recesses limiting the range of sliding of the shutter.